For the transmission of data in transport networks, nowadays systems are mainly employed that operate in accordance with the recommendations of ITU-T for SDH (Synchronous Digital Hierarchy) and SONET (Synchronous Optical Network). In these systems, payload-data signals to be transmitted are packeted into multiplex units and interleaved in accordance with a multiplex rule to form a time-division-multiplexed communications signal. This is then transmitted as an optical communications signal via optical fibers of the network, whereby in interposed network elements of the transport network the communications signals are disassembled into the individual multiplex units contained therein and can be interleaved again in a new configuration. Connections in an SDH-based or SONET-based transport network are switched in this way. An overview of these systems is presented, for example, in the article entitled “SONET 101” produced by Nortel Networks, which can be downloaded on the Internet from www.nortel.com/broadband/pdf/sonet 101.pdf.
In addition, optical networks are also increasingly finding application in which wavelength-multiplexed optical communications signals are transmitted. Such wavelength-multiplexed signals consist of several optical channels which are each represented by one wavelength. As a result, it is possible for several optical signals to be transmitted in parallel via a single optical waveguide. For such optical networks, network elements are required that are capable of decoupling individual wavelengths from and inserting them into wavelength-multiplexed communications signal (add/drop multiplexers). In addition, network elements are required that are able to disassemble such wavelength-multiplexed communications signals into the individual wavelengths contained therein and multiplex them again in a new configuration, in order to switch connections in the optical network (cross-connects). The realisation of the network elements that have been described is technically very elaborate, and the development of these devices is currently still in its initial stages. A standard for the optical channels is currently still being developed. For instance, a new multiplex hierarchy with the designation “optical channel (OCh)” is currently being discussed. This new multiplex hierarchy is intended to have multiplex levels with bit rates of 2.66 Gbit/sec and also multiples thereof (factors of four), namely 10.7x Gbit/sec and 43.x Gbit/sec, and is provided for optical transmission of information using wavelength-division multiplexing (WDM).
Furthermore, so-called optical cross-connects are currently being developed which are intended to switch optical communications signals of arbitrary format such as SONET, ATM, IP. They contain a central space-division switching matrix which is intended to be transparent in respect of the communications signals to be switched. An example of such an optical cross-connect is specified in the article entitled “Cost Effective Optical Networks: The Role of Optical Cross-Connects” by Charles A. Brackett, which can be downloaded on the Internet from the site www.tellium.com. This optical cross-connect operates with a SONET-based, clocked electrical space-division switching matrix which operates with the frame timing of OC-48. Full transparency in respect of non-SONET-based communications signals is therefore not guaranteed.
A further example is the 20000 Series wavelength router produced by Monterey. In a brochure relating to this product which has been published on the Internet it is specified that said router consists of a subsystem designated as a “switch core” and of I/O cards that support OC-48/STM-16 signals and that are connected to the switch core via short-range optical interfaces (Ultra-Short-Reach-Optics™). The switch core has a switching capacity of 256 OC-48 or 64 OC-192 equivalents. Consequently it is likewise based on the frame-timing rate of SONET and is therefore not fully transparent in respect of all signal-types.
One object of the present invention therefore consists in specifying an optical cross-connect that operates independently of bit rate and independently of protocol and additionally guarantees transmission functions for at least one protocol-type. A further object of the invention consists in specifying a method for bit-rate-independent and protocol-independent switching of optical communications signals.